The test for any line is whether it says what is wrong or how to fix it. The UK government's service manual makes the same point about user needs: describe the problem, such as needing a reminder, rather than a solution, such as an email, because the second may rule out a better answer.
Two things belong in a brief even though they feel awkward: what is explicitly out of scope, and who has the final say. A competitor link is fine if you add a line on what you admire and what you do not want copied.
A brief is a first draft that a studio is expected to question, so mark what you are unsure of instead of presenting it as fixed.
Updated October 2026
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